It is normal to manufacture knit fabrics on circular knitting machines to thereby produce a continuous knit tube of fabric to be finished as necessary for the end user.
However it is at times desirable to open the tube and utilize the opened knit fabric in many instances. For example flat or open width knit fabric is useful in the case where printed fabrics are required and also where laminated and coated fabrics are to be the end products.
In certain instances a guide line is created in the fabric so that a sensing device can be disposed to follow the guide to present the fabric to a slitter or cutting member whereby the knit tube is continuously cut and may then be laid open so that the vertical wales of the knit tube of fabric are square or at right angles to the courses of the knit fabric. At other times it is more beneficial to slit or cut the knit tube at random disregarding the squareness of the wales to the courses.
As is known knitted fabric is easily deformed and is normally subject to internal stresses in the stitches of the yarn. This is particularly evident during the slitting of a knit tube of fabric as it is being moved before during and after the slitting procedure wherein drag on the tube causes tension in the fabric which in turn causes greater shrinkage in the products made from the open or flat fabric.
To improve the effectiveness of such slitting devices usually more consideration is given to the speed of cutting rather then to the creation of an end product that is cut efficiently but at the same time with minimized tension of the fabric to end up with lesser shrinkage potential.
Increased cutting speed resulted from the development of a cage like member with a sensing means and knife incorporated into the unit as integral parts which facilitated the flow of the knit fabric tube over the cage so that it was more easily opened and at the same time presented the fabric for cutting. Such an arrangement is shown in U.S. Pat. No. 3,864,794 to Baumann.
The Baumann concept has been incorporated by Bianco s.p.a. Localita Vaccheria, 7/2; 12051 Alba (C/N) Italy in a slitter which operates to provide knit fabric in tube form from a station to a squeezer. The fabric tube moves upwardly to a detwister and then downwardly to a cage which is disposed to receive the tube of fabric along a substantially vertical axis thereof. The fabric which has been cut may then be moved to another station. The slitter is shown in the Bianco s.p.a. undated catalog N. 5.
While the Bianco apparatus may be effective in slitting on a guide line at high speed it induces an abnormal amount of tension in the fabric. In order for the sensing device to track properly the cage has to be expanded to keep the fabric flat and free of wrinkles and a uniform distance away from the sensing head which follows the cutting guide on the fabric.
The draw roll that pulls the fabric over the cage tends to contact the fabric tube causing more drag and longitudinal tension to cause elongation of the fabric which is undesirable as shrinkage potential is higher.